I fully support this suggestion - if you as an autocannon vehicle (SPAAG or armored car, doesn’t matter) or some other vehicle with a weak cannon runs into something you frontally cannot pen, and you did not plan any kind of escape route should things go south, you should get destroyed if the opponent is able to aim. Simple as that - you made a mistake, you don’t deserve a guaranteed means to cheat death.
SPAAGs which cannot hose down tank barrels to stop them from firing would now be much less of a problem, as would all autocannon light tanks. If this causes their BRs to go down, that is a good thing.
Overtiered heavy tanks like the Jumbos everyone loves to scream about when someone so much as thinks about changing either barrel damage or cupola shot stupidity would also go down in BR due to no longer being able to cheat their way out of situations they otherwise would have died in. Thus this change would help, not harm heavies with weak guns for their BR range in the long run. Besides the Jumbo Shermans, the Churchill Mk. VIIs, A.33 Excelsior, ALR-44 (ACL-1), and others also qualify for the same reason.